The story is all too familiar. An introduced landscape plant like Japanese knotweed has “escaped cultivation” and taken root elsewhere, uninvited. A foreign insect like the emerald ash borer has mysteriously appeared and seems to be spreading inexorably. We are earnestly warned that they are “wreaking ecological havoc” and reputedly costing someone millions or even billions of dollars. We react as if we’re under attack, readily applying the label “invaders” to our unwitting tormentors, as if they collectively had it in for us.

Personifying and demonizing the unfamiliar may help direct our dismay, but we hardly need science for that. When scientists focus on provoking public alarm, our science becomes blurred. Science can help work out the ways people move organisms, and investigate why some introduced populations fail while others grow. The demonizing reflex muddles our recommendations regarding which of these cases we can and should do something about.

In the early 1830s, British botanists began distinguishing between species known to have been introduced to an area by people and those without such a history. By the late 1840s the terms “alien” and “native” had been adopted, and a century later, those labels gained moral force with the rise of environmentalism: natives were natural, innocent, untainted by human association; aliens, like their human enablers, had detrimental “impacts,” not effects. Defense against “biological invasions” became a prominent goal of conservation biologists, who decided by acclamation that ”invasive” alien species were a dire threat to biodiversity.

Devil's claw (Martynia annua)

WIKIMEDIA COMMONS, MARCO SCHMIDT

But judging non-native species by their “lack” of “native” status is unfounded. First, the concept of nativeness lacks reliable ecological content—it simply means that a species under scrutiny has no known history of human-mediated dispersal. And second, not all introductions are so dramatically detrimental as the examples popularized by conservationists and the media. The devil’s claw, for example, a plant “native” to Mexico and surrounding regions, has had no discernible effects on Australia’s existing flora or fauna, despite being recently condemned as a threat to the continent’s biodiversity—long after its introduction in 1860s.

More importantly, sometimes introduced species that persist over decades or centuries become integral to local plant and animal communities, especially so where we have re-engineered the landscape or hydrology to generate an unprecedented environment. Attempting to extract non-natives from such areas may actually destabilize an ecosystem. Consider the tamarisk trees of the southern US plains and deserts. In the early 20th century, academics and government agencies encouraged farmers to plant these Old World trees and shrubs for livestock shade and erosion control. Meanwhile, as the Bureau of Reclamation completely reordered the region’s hydrology with storage and diversion dams, the native riparian woodlands were devastated. The hardier tamarisk trees survived, however, and spread to fill the breach. Since about 1940, an array of federal agencies and environmental groups have spent uncounted hundreds of millions of dollars waging war on tamarisk, despite the fact that ecologists have no idea what would replace it should they succeed. The tamarisk has demonstrated its fitness under now-prevailing conditions, and has become a vital riparian ecosystem component even while the war against it continues.

Conversely, routinely favoring “natives” hardly guarantees desirable outcomes. Almost all agricultural plants and domesticated animals were introduced to the places they now grow, and many face significant native pests. After South American potato plants were introduced to North America, for example, they encountered a resilient native insect now known as the Colorado potato beetle. Bringing potatoes to the insect’s native range created a new association between a crop and an insect, turning the once inconsequential beetles into pests. Any sentiment to save the native beetles from the impacts of potato farming is swamped by calls to save potato farmers from the beetles.

Tamarisk tree

WIKIMEDIA COMMONS, JERZY OPIOLA

Thus, neither a blanket condemnation nor a broad endorsement of any species based primarily on its origin or mode of transportation to now-occupied habitats is a sensible approach to safeguarding the world’s biodiversity or its food supply. Regardless of ”nativeness,” ecologists, policy makers, and conservationists should work to exclude potentially harmful pests. But they need to consider all the costs and benefits of every case on its own merits, in its specific context.

We briefly outlined these arguments in a commentary published in Naturethis past June, along with 17 other experienced conservationists (including Joan Ehrenfeld, who passed away June 25 after a year-long illness). A few weeks later, Nature published four reactions (one with 141 signatories, referred to below as “the 141 letter”) that were echoed in some respects by others we received in direct correspondence. Rather than respond to each letter individually (and repetitively), we have attempted to compile them into general objections to which we can make general responses.

Objection 1:We set up and assailed “straw men.”

Our assertion that “invasion biologists and conservationists” generally “oppose non-native species per se,” and our suggestion that the same folks “ignore the benefits of introduced species,” were met with much contention. But we stand by our statements. Invasion biologists and conservationists are a diverse lot, but historically and continuing to the present, they have broadly conflated the relatively descriptive terms introduced, alien, or nonnative species with the more conceptually troubled metaphorical indictment—“invasive species.”

Invasion biologists (none call themselves “introduction” biologists) do seem to recognize the problem, having repeatedly published glossaries that encourage a distinction between merely “introduced” and problematic “invasive” species. But most do not abide by these guidelines. Indeed, even the 141 letter fails to maintain this distinction by hoping that “for some introductions [not some invasions], eradication is possible.”

Still, the authors maintain that invasion biologists do acknowledge beneficial introduced species, arguing that “nobody tries to eradicate wheat”—a globally widespread crop that was disseminated from the Near East. But some restorationists would certainly replace wheat with “native” grassland if given the means and the opportunity. Regardless, the example simply deflects from our point. Our concern is not primarily focused on forcibly maintained monocultures, but with all ecosystems that are now and foreseeably structured in some part by human agency.

Objection 2: The high evolutionary fitness of introduced species signified by their rapid population growth does not guarantee long-term fitness so it should not be taken as evidence of ecological belonging.

Despite its framing, this objection is primarily concerned with human scale stability and continuity. Many ecologists still presume that natural changes occur only at imperceptible rates and that all “good” ecological relationships are permanent and sustain beneficial community functions. But interactions between organisms and their environments are ecological, regardless of how they came to exist, or how long they persist. Evolutionary fitness is a matter of reproductive success under prevailing conditions, even if those conditions are, from a human perspective, “unnatural.” Conversely, when we seek to modulate fitness to conserve threatened or endangered species, or to eradicate so-called “pests,” we are judging whether an ecological interaction should happen with economic, legal, moral, ethical, aesthetic or cultural criteria. As such, these sorts of manipulations are based purely on human constructs, and should not be mistaken for laws or objectives of nature.

Objection 3: Invasion biology is not worthless.

The authors of one published reaction contended we had implied that invasion biologists had made no useful contributions to ecological knowledge. We made no such claim. But invasion biology, like epidemiology, is a discipline explicitly devoted to destroying that which it studies. This necessarily constrains its research program and colors its communications, both internal and external, in very particular ways. We believe, then, that less confrontational, more objective research approaches have greater potential to produce valuable results.

Objection 4: Our supposed contention that potential invaders are easily identifiable soon after detection, so management circumspection is unnecessary, even harmful, is false.

Like objection 3, this assertion extends our claims by implication. We did not categorically object to programs aimed at preventing introductions or eradicating populations of introduced species when it can be done in a dependable, highly targeted manner.

What we object to is an insistence on permanent, hopeless wars on well- and widely-established non-native taxa, conflicts that continuously disrupt ecosystems where introduced species now play significant ecological roles. Furthermore, as long as the many modes of inter- and trans-continental shipping continue to operate, organisms will unexpectedly move along with materials, goods, and people. Thus, although we respect the values inspiring many local conservation and restoration efforts, we caution that continuous “weeding” creates a further, more permanent dependence on human judgment and activity rather than a lesser, more temporary one.

In summary, our motivations echo those of more familiar forms of biodiversity conservation. Our primary goals are better understanding and managing human ecological influences. The approaches we suggest are no easier than those currently being practiced, as understanding and predicting community ecology will continue to challenge our discipline. However, we believe that more careful framing will permit more realistic characterizations of ecosystems, and better inform the multifarious and often inconsistent motivations underlying management interventions. Hence we wrote to expose and open a very practical debate to a wider array of participants. We are pleased that, in addition to the published responses, we have individually received many thoughtful and interesting comments from readers worldwide, and we look forward to continued discussion that might lead to more united conservation efforts.

Matthew K. Chew is an arid lands riparian ecologist and historian of biology at Arizona State University. His experiences coordinating Arizona’s State Natural Areas Program led him to study conceptions of biotic nativeness and belonging. Scott P. Carroll is at the University of California, Davis, and the director of the new Institute for Contemporary Evolution. Observing native insects evolve to exploit introduced plants underlies his belief in the value of evolutionary management in communities of mixed nativeness. This opinion piece expands on a June 2011 commentary in Nature, and aims to respond to a few ensuing reactions, some of which were published as correspondence in Nature in July.

Comments

Thanks for the article -- I'm going to circulate it among our biology faculty!

However, as a public-health-trained biologist,Â I do take issue with one small point: "But invasion biology, like epidemiology, is a discipline explicitly devoted to destroying that which it studies." Epidemiology is not explicitly devoted to destroying that which it studies (the implication being that it only studies disease). The WHO defines health as NOT merely an "absence of disease" ("Health is a state of complete physical, mental, and social well-being and not merely the absence of disease or infirmity."). Epidemiology studies patterns of health in populations, including factors that impact health.Â Often, those are factors directly related to disease -- but not always.

It seems to me though, that while not always the case,Â most adaptation to environment is done over very long periods of time within a complex and integrated system.Â This seems beneficial in that the interconnection of the sysem would add ecological stability.Â So while not every non-native species absolutely needs to be stopped, there ceartainly needs to beÂ an effortÂ to limit intorduction of non-native species as much as possible.

I live in Iowa were very little native evironment exists, and the small amounts left seem very sensitive to be dominated byÂ non-native invasion.Â I think it isÂ worth saving these fragile enviroments for both ecological reasons, and just for reasons of heritage and quality of life.Â If we have to err on one side or the other in terms of judgements we make on plants, I would rather see us err on the side of being overconcerned, becuase there is potential for great damage to an environment that can not be predicted unitl it happens.

I don't think we should be paranoid, but at the same time we should not ignore the fact that most plants do adapt to their environments over very long periods, there is benifit to the envorinment in this, and humans have great potential to negatively impact enivironments with things such as non native species.Â I think that concern is founded.

I'd invite you to consider the case of an invasive like garlic mustard which is causing devastation to the woodland and savannah habitats of the east and midwest.Â The high density growth and rapid spread of invasives such as this leads to loss of all small low growing plants in these environments- literally dozens of species.Â This is all too common with invasives.Â If we don't work to eradicate such plants from at least local preserves the loss of biodiversity would be a crushing blow to those who care about their local environments, which should include just about everyone. When species form monocultural replacements of existing plant biodiversity animal biodiversity must follow.Â That said, I think the solution lies not in top down, governmental eradication approaches but in bottom up community organized control efforts.Â The solution is too big and serious to leave in the hands of the government.

I vaguely recall reading a paper that came out several years ago exploring the impact of animal "invasives". Â If memory serves the paper concluded that fully nine out of ten introduced species found unoccupied niches, vanishing into the biosphere without displacing other species. Â You could argue that their effect was positive in that they parallelized the predator-prey networks. Â I have never heard of a comparable paper being done for plants but if someone was to post a persuasive proposal for such a project on Kickstarter I would contribute to it.Â

I certainly agree that diabolising all "invasives" seems a strange thing to do. After all, we know that species are being exchanged between regions all the time. The story of the snake or the frog or the bug or the plant or the whatever travelling on a log from one island or even continent to another is a classic. While I am aware of the difference between a human and a log, I fail to see the importance of that difference. Some species introduced by humans will becomes invasives, some will die out, and others will do something in between. What reasons do we have to assume this will be different in case of non-human mediated introductions?

I also agree with Sara M Volk that the description of epidemiology seems somewhat narrow.

I am not sure if these conclusions apply universally. New Zealand faces a multitude of invasions every year - from Southern Swamp mosquitoes (malaria!) to snakes and Argentinian ants and Nasella tussock! Â Of the 650 species of alien birds introduced here only very few, about 16, "took", so there is strong resilience in native communities. Â But those that do succeed in invading can be devastating. Â Brown top grass is devastating the high country and causing the extinction of previously common species ("rare" species do not seem to be affected so much). Â Old Man's Beard clematis is a terrible threat to precious lowland temperate rain forest. And I could go on and on. Â So, I do not think you would find much support for cessation of attempts to protect our biodiversity or for attempts to lessen our fight (and it is a fight) against invasive pests introduced in ever increasing numbers due to globalization of world trade.

We view useful species, such as brown top, as having their place, but that place is not where they can devastate our precious and unique flora and fauna. Â Most pests can only establish themselves in human-induced environments or in severely damaged native communities. Â

And new technologies, such as automatic rodent traps are enabling us to take a "strong" approach to conservation. Â For example,Â in getting rid of key rodent pests, something we could only dream of a few years ago. Â We can now restore many communities to their previous rodent-free condition. Â The results are astounding, even in small reserves such as Riccarton Bush, in the heart of a city. Â This reserve has the only stand of swamp podocarp forest left, so is well worth making every effort and regarding every alien species as a target for destruction. Â

We feel that if we let up on the fight to conserve we may lose the battle since new technologies will not be developed that may enable us to reach our twin goals of restoration and protection.

You seem to have mistaken natural movement to unnatural movement when people either release either fauna or flora by mistake or by design, take Cane toads Bufo marinus australia is reaping the catastrophy of having this species free to roam.Whilst bird and animal species do migrate they have a slower effect as their numbers are generally smaller, but when dumped species are let go then niches are disrupted and things start to fall apart, Bees for example the Acarine mite is plauging most collonys now, If bees die out we are in BIG Trouble, I work with an invasive species and let me tell you, the scientists are not jopking when they say that niches and endemic species are under attack from invasive species.but you know the most invasive species of all MAN.

Thanks for the article -- I'm going to circulate it among our biology faculty!

However, as a public-health-trained biologist,Â I do take issue with one small point: "But invasion biology, like epidemiology, is a discipline explicitly devoted to destroying that which it studies." Epidemiology is not explicitly devoted to destroying that which it studies (the implication being that it only studies disease). The WHO defines health as NOT merely an "absence of disease" ("Health is a state of complete physical, mental, and social well-being and not merely the absence of disease or infirmity."). Epidemiology studies patterns of health in populations, including factors that impact health.Â Often, those are factors directly related to disease -- but not always.

It seems to me though, that while not always the case,Â most adaptation to environment is done over very long periods of time within a complex and integrated system.Â This seems beneficial in that the interconnection of the sysem would add ecological stability.Â So while not every non-native species absolutely needs to be stopped, there ceartainly needs to beÂ an effortÂ to limit intorduction of non-native species as much as possible.

I live in Iowa were very little native evironment exists, and the small amounts left seem very sensitive to be dominated byÂ non-native invasion.Â I think it isÂ worth saving these fragile enviroments for both ecological reasons, and just for reasons of heritage and quality of life.Â If we have to err on one side or the other in terms of judgements we make on plants, I would rather see us err on the side of being overconcerned, becuase there is potential for great damage to an environment that can not be predicted unitl it happens.

I don't think we should be paranoid, but at the same time we should not ignore the fact that most plants do adapt to their environments over very long periods, there is benifit to the envorinment in this, and humans have great potential to negatively impact enivironments with things such as non native species.Â I think that concern is founded.

I'd invite you to consider the case of an invasive like garlic mustard which is causing devastation to the woodland and savannah habitats of the east and midwest.Â The high density growth and rapid spread of invasives such as this leads to loss of all small low growing plants in these environments- literally dozens of species.Â This is all too common with invasives.Â If we don't work to eradicate such plants from at least local preserves the loss of biodiversity would be a crushing blow to those who care about their local environments, which should include just about everyone. When species form monocultural replacements of existing plant biodiversity animal biodiversity must follow.Â That said, I think the solution lies not in top down, governmental eradication approaches but in bottom up community organized control efforts.Â The solution is too big and serious to leave in the hands of the government.

I vaguely recall reading a paper that came out several years ago exploring the impact of animal "invasives". Â If memory serves the paper concluded that fully nine out of ten introduced species found unoccupied niches, vanishing into the biosphere without displacing other species. Â You could argue that their effect was positive in that they parallelized the predator-prey networks. Â I have never heard of a comparable paper being done for plants but if someone was to post a persuasive proposal for such a project on Kickstarter I would contribute to it.Â

I certainly agree that diabolising all "invasives" seems a strange thing to do. After all, we know that species are being exchanged between regions all the time. The story of the snake or the frog or the bug or the plant or the whatever travelling on a log from one island or even continent to another is a classic. While I am aware of the difference between a human and a log, I fail to see the importance of that difference. Some species introduced by humans will becomes invasives, some will die out, and others will do something in between. What reasons do we have to assume this will be different in case of non-human mediated introductions?

I also agree with Sara M Volk that the description of epidemiology seems somewhat narrow.

I am not sure if these conclusions apply universally. New Zealand faces a multitude of invasions every year - from Southern Swamp mosquitoes (malaria!) to snakes and Argentinian ants and Nasella tussock! Â Of the 650 species of alien birds introduced here only very few, about 16, "took", so there is strong resilience in native communities. Â But those that do succeed in invading can be devastating. Â Brown top grass is devastating the high country and causing the extinction of previously common species ("rare" species do not seem to be affected so much). Â Old Man's Beard clematis is a terrible threat to precious lowland temperate rain forest. And I could go on and on. Â So, I do not think you would find much support for cessation of attempts to protect our biodiversity or for attempts to lessen our fight (and it is a fight) against invasive pests introduced in ever increasing numbers due to globalization of world trade.

We view useful species, such as brown top, as having their place, but that place is not where they can devastate our precious and unique flora and fauna. Â Most pests can only establish themselves in human-induced environments or in severely damaged native communities. Â

And new technologies, such as automatic rodent traps are enabling us to take a "strong" approach to conservation. Â For example,Â in getting rid of key rodent pests, something we could only dream of a few years ago. Â We can now restore many communities to their previous rodent-free condition. Â The results are astounding, even in small reserves such as Riccarton Bush, in the heart of a city. Â This reserve has the only stand of swamp podocarp forest left, so is well worth making every effort and regarding every alien species as a target for destruction. Â

We feel that if we let up on the fight to conserve we may lose the battle since new technologies will not be developed that may enable us to reach our twin goals of restoration and protection.

You seem to have mistaken natural movement to unnatural movement when people either release either fauna or flora by mistake or by design, take Cane toads Bufo marinus australia is reaping the catastrophy of having this species free to roam.Whilst bird and animal species do migrate they have a slower effect as their numbers are generally smaller, but when dumped species are let go then niches are disrupted and things start to fall apart, Bees for example the Acarine mite is plauging most collonys now, If bees die out we are in BIG Trouble, I work with an invasive species and let me tell you, the scientists are not jopking when they say that niches and endemic species are under attack from invasive species.but you know the most invasive species of all MAN.

Thanks for the article -- I'm going to circulate it among our biology faculty!

However, as a public-health-trained biologist,Â I do take issue with one small point: "But invasion biology, like epidemiology, is a discipline explicitly devoted to destroying that which it studies." Epidemiology is not explicitly devoted to destroying that which it studies (the implication being that it only studies disease). The WHO defines health as NOT merely an "absence of disease" ("Health is a state of complete physical, mental, and social well-being and not merely the absence of disease or infirmity."). Epidemiology studies patterns of health in populations, including factors that impact health.Â Often, those are factors directly related to disease -- but not always.

It seems to me though, that while not always the case,Â most adaptation to environment is done over very long periods of time within a complex and integrated system.Â This seems beneficial in that the interconnection of the sysem would add ecological stability.Â So while not every non-native species absolutely needs to be stopped, there ceartainly needs to beÂ an effortÂ to limit intorduction of non-native species as much as possible.

I live in Iowa were very little native evironment exists, and the small amounts left seem very sensitive to be dominated byÂ non-native invasion.Â I think it isÂ worth saving these fragile enviroments for both ecological reasons, and just for reasons of heritage and quality of life.Â If we have to err on one side or the other in terms of judgements we make on plants, I would rather see us err on the side of being overconcerned, becuase there is potential for great damage to an environment that can not be predicted unitl it happens.

I don't think we should be paranoid, but at the same time we should not ignore the fact that most plants do adapt to their environments over very long periods, there is benifit to the envorinment in this, and humans have great potential to negatively impact enivironments with things such as non native species.Â I think that concern is founded.

I'd invite you to consider the case of an invasive like garlic mustard which is causing devastation to the woodland and savannah habitats of the east and midwest.Â The high density growth and rapid spread of invasives such as this leads to loss of all small low growing plants in these environments- literally dozens of species.Â This is all too common with invasives.Â If we don't work to eradicate such plants from at least local preserves the loss of biodiversity would be a crushing blow to those who care about their local environments, which should include just about everyone. When species form monocultural replacements of existing plant biodiversity animal biodiversity must follow.Â That said, I think the solution lies not in top down, governmental eradication approaches but in bottom up community organized control efforts.Â The solution is too big and serious to leave in the hands of the government.

I vaguely recall reading a paper that came out several years ago exploring the impact of animal "invasives". Â If memory serves the paper concluded that fully nine out of ten introduced species found unoccupied niches, vanishing into the biosphere without displacing other species. Â You could argue that their effect was positive in that they parallelized the predator-prey networks. Â I have never heard of a comparable paper being done for plants but if someone was to post a persuasive proposal for such a project on Kickstarter I would contribute to it.Â

I certainly agree that diabolising all "invasives" seems a strange thing to do. After all, we know that species are being exchanged between regions all the time. The story of the snake or the frog or the bug or the plant or the whatever travelling on a log from one island or even continent to another is a classic. While I am aware of the difference between a human and a log, I fail to see the importance of that difference. Some species introduced by humans will becomes invasives, some will die out, and others will do something in between. What reasons do we have to assume this will be different in case of non-human mediated introductions?

I also agree with Sara M Volk that the description of epidemiology seems somewhat narrow.

I am not sure if these conclusions apply universally. New Zealand faces a multitude of invasions every year - from Southern Swamp mosquitoes (malaria!) to snakes and Argentinian ants and Nasella tussock! Â Of the 650 species of alien birds introduced here only very few, about 16, "took", so there is strong resilience in native communities. Â But those that do succeed in invading can be devastating. Â Brown top grass is devastating the high country and causing the extinction of previously common species ("rare" species do not seem to be affected so much). Â Old Man's Beard clematis is a terrible threat to precious lowland temperate rain forest. And I could go on and on. Â So, I do not think you would find much support for cessation of attempts to protect our biodiversity or for attempts to lessen our fight (and it is a fight) against invasive pests introduced in ever increasing numbers due to globalization of world trade.

We view useful species, such as brown top, as having their place, but that place is not where they can devastate our precious and unique flora and fauna. Â Most pests can only establish themselves in human-induced environments or in severely damaged native communities. Â

And new technologies, such as automatic rodent traps are enabling us to take a "strong" approach to conservation. Â For example,Â in getting rid of key rodent pests, something we could only dream of a few years ago. Â We can now restore many communities to their previous rodent-free condition. Â The results are astounding, even in small reserves such as Riccarton Bush, in the heart of a city. Â This reserve has the only stand of swamp podocarp forest left, so is well worth making every effort and regarding every alien species as a target for destruction. Â

We feel that if we let up on the fight to conserve we may lose the battle since new technologies will not be developed that may enable us to reach our twin goals of restoration and protection.

You seem to have mistaken natural movement to unnatural movement when people either release either fauna or flora by mistake or by design, take Cane toads Bufo marinus australia is reaping the catastrophy of having this species free to roam.Whilst bird and animal species do migrate they have a slower effect as their numbers are generally smaller, but when dumped species are let go then niches are disrupted and things start to fall apart, Bees for example the Acarine mite is plauging most collonys now, If bees die out we are in BIG Trouble, I work with an invasive species and let me tell you, the scientists are not jopking when they say that niches and endemic species are under attack from invasive species.but you know the most invasive species of all MAN.

Thank you for publishing this article and to Professors Chew and Carroll for writing it.Â Although many scientists share their opinion of â€œinvasion biology,â€쳌 few are willing to say so publically because of the personal attacks they provoke.Â I know because I have been struggling against the destruction of our public lands by native plant advocates in the San Francisco Bay Area for over 12 years.Â Millions of non-native trees are being destroyed here.Â Our public parks are being sprayed with dangerous herbicides.Â Our air is being polluted and our homes endangered by prescribed burns used to destroy non-native vegetation and promote germination of native species.Â The native plant movement has a death grip on our public lands.Â My objection to these destructive practices has resulted in constant harassment by those who make their living on these â€œrestorations.â€쳌Â It is now an industry, with deeply imbedded financial interest to continue this futile war on non-native species.I have made good use of Professor Carrollâ€™s research to help to make the case against nativism and I am grateful to him for his research.Â Please visit the Million Trees blog to read about Professor Carrollâ€™s research:Â http://milliontrees.wordpress.....Â He tells us about the rapid evolution of insects in response to new plant species.Â One of many unscientific assumptions of nativists is that introduced plants are always invasive because they have no insect predators, based on their simplistic and conflated understanding of â€œco-evolution.â€쳌

Thank you for publishing this article and to Professors Chew and Carroll for writing it.Â Although many scientists share their opinion of â€œinvasion biology,â€쳌 few are willing to say so publically because of the personal attacks they provoke.Â I know because I have been struggling against the destruction of our public lands by native plant advocates in the San Francisco Bay Area for over 12 years.Â Millions of non-native trees are being destroyed here.Â Our public parks are being sprayed with dangerous herbicides.Â Our air is being polluted and our homes endangered by prescribed burns used to destroy non-native vegetation and promote germination of native species.Â The native plant movement has a death grip on our public lands.Â My objection to these destructive practices has resulted in constant harassment by those who make their living on these â€œrestorations.â€쳌Â It is now an industry, with deeply imbedded financial interest to continue this futile war on non-native species.I have made good use of Professor Carrollâ€™s research to help to make the case against nativism and I am grateful to him for his research.Â Please visit the Million Trees blog to read about Professor Carrollâ€™s research:Â http://milliontrees.wordpress.....Â He tells us about the rapid evolution of insects in response to new plant species.Â One of many unscientific assumptions of nativists is that introduced plants are always invasive because they have no insect predators, based on their simplistic and conflated understanding of â€œco-evolution.â€쳌

Thank you for publishing this article and to Professors Chew and Carroll for writing it.Â Although many scientists share their opinion of â€œinvasion biology,â€쳌 few are willing to say so publically because of the personal attacks they provoke.Â I know because I have been struggling against the destruction of our public lands by native plant advocates in the San Francisco Bay Area for over 12 years.Â Millions of non-native trees are being destroyed here.Â Our public parks are being sprayed with dangerous herbicides.Â Our air is being polluted and our homes endangered by prescribed burns used to destroy non-native vegetation and promote germination of native species.Â The native plant movement has a death grip on our public lands.Â My objection to these destructive practices has resulted in constant harassment by those who make their living on these â€œrestorations.â€쳌Â It is now an industry, with deeply imbedded financial interest to continue this futile war on non-native species.I have made good use of Professor Carrollâ€™s research to help to make the case against nativism and I am grateful to him for his research.Â Please visit the Million Trees blog to read about Professor Carrollâ€™s research:Â http://milliontrees.wordpress.....Â He tells us about the rapid evolution of insects in response to new plant species.Â One of many unscientific assumptions of nativists is that introduced plants are always invasive because they have no insect predators, based on their simplistic and conflated understanding of â€œco-evolution.â€쳌

Well, I disagree with the last sentence here. Â I deliberately plant natives on my land because, as shown by the leaves riddled with holes, they have manner local insects that feed upon them. Â That is what I want. Â My Carolina Cherry Laurels (native) provide great forage and habitat, but my English Laurels (I'll probably remove them) are a desert by comparison!

Well, I disagree with the last sentence here. Â I deliberately plant natives on my land because, as shown by the leaves riddled with holes, they have manner local insects that feed upon them. Â That is what I want. Â My Carolina Cherry Laurels (native) provide great forage and habitat, but my English Laurels (I'll probably remove them) are a desert by comparison!

Well, I disagree with the last sentence here. Â I deliberately plant natives on my land because, as shown by the leaves riddled with holes, they have manner local insects that feed upon them. Â That is what I want. Â My Carolina Cherry Laurels (native) provide great forage and habitat, but my English Laurels (I'll probably remove them) are a desert by comparison!

With plants like Kudzu overrunning the countryside in the southeastern United States, even topping small trees, the damage that can be caused by invasives is obvious. Â Native plant species harbor a native community of plant feeders and a complex web of interactions between these and their predators, parasites, pathogens, etc. Â These controls are generally lacking for many introduced species, although certainly not all! Â I think that in time control agents for plants like Kudzu may evolve locally, but this may take many of our lifetimes! Â Whole continents of fauna like Australia can be threatened by introductions. Â Without control, introduced goats in the Galapagos would rapidly drive the tortoises there to extinction. Â At the same time, I think the greater threat in my area lies in the lack of any significant grazers to control forestation and allow the prairies to survive, so the introduction of grazing antelope from Africa would probably be a boon. Â Also, we need a replacement for the Carolina Parakeet to distribute seeds. Â And where are those predators that are supposed to be controlling the deer population, so that they leave something for the beavers, so the beavers can survive and provide habitat for ducks, panfish, etc.? Â Life out of balance, but can selective introductions help things?

I realise that Chew and Carroll's comments are controversial, but I can't help but having the impression that most of the controversy is rooted in a misunderstanding of what they wrote. Chew and Carroll are mainly pointing out that there is a difference between biology as a science, and conservation (including weeding out invasives).

Yes, indeed, invasives can be pretty invasive. Dog-strangling vine, Kudzu, Japanese knotweed, European starlings, rats, mute swans, the list goes on and on. But it doesn't stop there. What about native species that become far more successful than they used to be? Toronto is now considered the raccoon capital of the world, for example, but we also have a gazillionplex of grey squirrels and cowbirds to name but three of the best-known ones.

Biodiversity is great, especially for those of us who are interested in biodiversity. The rest of the world doesn't really care, and I can't help but wonder if investing massive resources in weeding out invasives is really the way to go. After all, even big problems such as cane toads are bound to be self-limiting.Â

Overpopulation and lack of resources will eventually start to limit invasions, and these animals or plants or whatever will start to die off without our help. Also, protecting biodiversity has a bit of a hypocritical ring to it. Most of us love to protect polar bears, pandas and beavers, far fewer agree to spend resources protecting spiders, snakes and leaches, and I can't remember the last time I met someone who was intent on protecting mosquitoes, wasps, measles and ebola. Yet, they too are part of our beloved biodiversity, are they not?

Let's also not forget that there is far more that we don't know than that we do know, and that well-meaning interventions to protect biodiversity may well be having the opposite effect.

I wonder if it is not better to simply limit human intervention to protecting existing natural areas against human colonisation and exploitation andÂ to let nature (including invasives) run its course.Â

The dodo and the Tasmanian wolf no longer exist. That is too bad, I would have loved to see them. They seemed quite fascinating. But reality seems to indicate that "nature" doesn't really miss them.

With plants like Kudzu overrunning the countryside in the southeastern United States, even topping small trees, the damage that can be caused by invasives is obvious. Â Native plant species harbor a native community of plant feeders and a complex web of interactions between these and their predators, parasites, pathogens, etc. Â These controls are generally lacking for many introduced species, although certainly not all! Â I think that in time control agents for plants like Kudzu may evolve locally, but this may take many of our lifetimes! Â Whole continents of fauna like Australia can be threatened by introductions. Â Without control, introduced goats in the Galapagos would rapidly drive the tortoises there to extinction. Â At the same time, I think the greater threat in my area lies in the lack of any significant grazers to control forestation and allow the prairies to survive, so the introduction of grazing antelope from Africa would probably be a boon. Â Also, we need a replacement for the Carolina Parakeet to distribute seeds. Â And where are those predators that are supposed to be controlling the deer population, so that they leave something for the beavers, so the beavers can survive and provide habitat for ducks, panfish, etc.? Â Life out of balance, but can selective introductions help things?

I realise that Chew and Carroll's comments are controversial, but I can't help but having the impression that most of the controversy is rooted in a misunderstanding of what they wrote. Chew and Carroll are mainly pointing out that there is a difference between biology as a science, and conservation (including weeding out invasives).

Yes, indeed, invasives can be pretty invasive. Dog-strangling vine, Kudzu, Japanese knotweed, European starlings, rats, mute swans, the list goes on and on. But it doesn't stop there. What about native species that become far more successful than they used to be? Toronto is now considered the raccoon capital of the world, for example, but we also have a gazillionplex of grey squirrels and cowbirds to name but three of the best-known ones.

Biodiversity is great, especially for those of us who are interested in biodiversity. The rest of the world doesn't really care, and I can't help but wonder if investing massive resources in weeding out invasives is really the way to go. After all, even big problems such as cane toads are bound to be self-limiting.Â

Overpopulation and lack of resources will eventually start to limit invasions, and these animals or plants or whatever will start to die off without our help. Also, protecting biodiversity has a bit of a hypocritical ring to it. Most of us love to protect polar bears, pandas and beavers, far fewer agree to spend resources protecting spiders, snakes and leaches, and I can't remember the last time I met someone who was intent on protecting mosquitoes, wasps, measles and ebola. Yet, they too are part of our beloved biodiversity, are they not?

Let's also not forget that there is far more that we don't know than that we do know, and that well-meaning interventions to protect biodiversity may well be having the opposite effect.

I wonder if it is not better to simply limit human intervention to protecting existing natural areas against human colonisation and exploitation andÂ to let nature (including invasives) run its course.Â

The dodo and the Tasmanian wolf no longer exist. That is too bad, I would have loved to see them. They seemed quite fascinating. But reality seems to indicate that "nature" doesn't really miss them.

With plants like Kudzu overrunning the countryside in the southeastern United States, even topping small trees, the damage that can be caused by invasives is obvious. Â Native plant species harbor a native community of plant feeders and a complex web of interactions between these and their predators, parasites, pathogens, etc. Â These controls are generally lacking for many introduced species, although certainly not all! Â I think that in time control agents for plants like Kudzu may evolve locally, but this may take many of our lifetimes! Â Whole continents of fauna like Australia can be threatened by introductions. Â Without control, introduced goats in the Galapagos would rapidly drive the tortoises there to extinction. Â At the same time, I think the greater threat in my area lies in the lack of any significant grazers to control forestation and allow the prairies to survive, so the introduction of grazing antelope from Africa would probably be a boon. Â Also, we need a replacement for the Carolina Parakeet to distribute seeds. Â And where are those predators that are supposed to be controlling the deer population, so that they leave something for the beavers, so the beavers can survive and provide habitat for ducks, panfish, etc.? Â Life out of balance, but can selective introductions help things?

I realise that Chew and Carroll's comments are controversial, but I can't help but having the impression that most of the controversy is rooted in a misunderstanding of what they wrote. Chew and Carroll are mainly pointing out that there is a difference between biology as a science, and conservation (including weeding out invasives).

Yes, indeed, invasives can be pretty invasive. Dog-strangling vine, Kudzu, Japanese knotweed, European starlings, rats, mute swans, the list goes on and on. But it doesn't stop there. What about native species that become far more successful than they used to be? Toronto is now considered the raccoon capital of the world, for example, but we also have a gazillionplex of grey squirrels and cowbirds to name but three of the best-known ones.

Biodiversity is great, especially for those of us who are interested in biodiversity. The rest of the world doesn't really care, and I can't help but wonder if investing massive resources in weeding out invasives is really the way to go. After all, even big problems such as cane toads are bound to be self-limiting.Â

Overpopulation and lack of resources will eventually start to limit invasions, and these animals or plants or whatever will start to die off without our help. Also, protecting biodiversity has a bit of a hypocritical ring to it. Most of us love to protect polar bears, pandas and beavers, far fewer agree to spend resources protecting spiders, snakes and leaches, and I can't remember the last time I met someone who was intent on protecting mosquitoes, wasps, measles and ebola. Yet, they too are part of our beloved biodiversity, are they not?

Let's also not forget that there is far more that we don't know than that we do know, and that well-meaning interventions to protect biodiversity may well be having the opposite effect.

I wonder if it is not better to simply limit human intervention to protecting existing natural areas against human colonisation and exploitation andÂ to let nature (including invasives) run its course.Â

The dodo and the Tasmanian wolf no longer exist. That is too bad, I would have loved to see them. They seemed quite fascinating. But reality seems to indicate that "nature" doesn't really miss them.

Just came across this article by chance. These blokes seem pathetic &Â lackÂ any vision, also very selective in their choice of species. - "permanent, hopeless wars on well- and widely-established non-native taxa" - what bullxxxt. (How did Chen become a professor with only half a dozen papers in less than high ranking journals? OK- 1 each in Nature & Science recently but only because controversial-not any substance.) Arizona obviously the place to go if you need an easy academic position. I'm in Australia & would love to hear a rationlisation for how rabbits, foxes & cats have enriched our environment. (I bury them under new tree plantings- gets some value). Introduced pasture plants & livestock I can live with- they are usually managed. We have eliminated lantana, groudsel, camphor laurel & rabbits from our property. All you need is the will & persistence. Governments & scientists might provide some useful advice & some $ for recognised conservation work, however generally useless when it comes to large scale control.Â Does Chew get funding as an apologist for why "it's all too hard". Hope they all appreciate the fire ants down "South". At least in Queensland there has been a concerted & ongoing effort to eliminate them before they become established. A world dominated by people, cockroaches, rats & similar vermin is not a world I want to live in. Fortunately I'll be fertilising a native tree by then.

Just came across this article by chance. These blokes seem pathetic &Â lackÂ any vision, also very selective in their choice of species. - "permanent, hopeless wars on well- and widely-established non-native taxa" - what bullxxxt. (How did Chen become a professor with only half a dozen papers in less than high ranking journals? OK- 1 each in Nature & Science recently but only because controversial-not any substance.) Arizona obviously the place to go if you need an easy academic position. I'm in Australia & would love to hear a rationlisation for how rabbits, foxes & cats have enriched our environment. (I bury them under new tree plantings- gets some value). Introduced pasture plants & livestock I can live with- they are usually managed. We have eliminated lantana, groudsel, camphor laurel & rabbits from our property. All you need is the will & persistence. Governments & scientists might provide some useful advice & some $ for recognised conservation work, however generally useless when it comes to large scale control.Â Does Chew get funding as an apologist for why "it's all too hard". Hope they all appreciate the fire ants down "South". At least in Queensland there has been a concerted & ongoing effort to eliminate them before they become established. A world dominated by people, cockroaches, rats & similar vermin is not a world I want to live in. Fortunately I'll be fertilising a native tree by then.

Just came across this article by chance. These blokes seem pathetic &Â lackÂ any vision, also very selective in their choice of species. - "permanent, hopeless wars on well- and widely-established non-native taxa" - what bullxxxt. (How did Chen become a professor with only half a dozen papers in less than high ranking journals? OK- 1 each in Nature & Science recently but only because controversial-not any substance.) Arizona obviously the place to go if you need an easy academic position. I'm in Australia & would love to hear a rationlisation for how rabbits, foxes & cats have enriched our environment. (I bury them under new tree plantings- gets some value). Introduced pasture plants & livestock I can live with- they are usually managed. We have eliminated lantana, groudsel, camphor laurel & rabbits from our property. All you need is the will & persistence. Governments & scientists might provide some useful advice & some $ for recognised conservation work, however generally useless when it comes to large scale control.Â Does Chew get funding as an apologist for why "it's all too hard". Hope they all appreciate the fire ants down "South". At least in Queensland there has been a concerted & ongoing effort to eliminate them before they become established. A world dominated by people, cockroaches, rats & similar vermin is not a world I want to live in. Fortunately I'll be fertilising a native tree by then.

As someone who has researched interactions between native and nonnative species, as well as taught an in-depth undergraduate course on the many issues associated with invasive species, here is my own take on the deficiencies of this essay:

As someone who has researched interactions between native and nonnative species, as well as taught an in-depth undergraduate course on the many issues associated with invasive species, here is my own take on the deficiencies of this essay:

As someone who has researched interactions between native and nonnative species, as well as taught an in-depth undergraduate course on the many issues associated with invasive species, here is my own take on the deficiencies of this essay:

marvellous. You have said what I was trying to say on Wild About Britain and was shouted down. I suppose I went one step further though. I suggested that deliberatly introducing critically endangered species to a new environment might save them. Of course environmental changes at their present site would have to be researched to see what sort of conditions they thrivedÂ in, in the past. Then if they were transferred toÂ a place with those conditions they might well recover.I also pointed out- perhaps wrongly, I am not sure. that introducing a rare species is far less likely to cause a problem than introducing a common one. In a new environment a rare species might thrive, but it will, because of its more limited gene pool, be less adaptable thanÂ a common species and so is unlikely to reach pest proportions.

marvellous. You have said what I was trying to say on Wild About Britain and was shouted down. I suppose I went one step further though. I suggested that deliberatly introducing critically endangered species to a new environment might save them. Of course environmental changes at their present site would have to be researched to see what sort of conditions they thrivedÂ in, in the past. Then if they were transferred toÂ a place with those conditions they might well recover.I also pointed out- perhaps wrongly, I am not sure. that introducing a rare species is far less likely to cause a problem than introducing a common one. In a new environment a rare species might thrive, but it will, because of its more limited gene pool, be less adaptable thanÂ a common species and so is unlikely to reach pest proportions.

marvellous. You have said what I was trying to say on Wild About Britain and was shouted down. I suppose I went one step further though. I suggested that deliberatly introducing critically endangered species to a new environment might save them. Of course environmental changes at their present site would have to be researched to see what sort of conditions they thrivedÂ in, in the past. Then if they were transferred toÂ a place with those conditions they might well recover.I also pointed out- perhaps wrongly, I am not sure. that introducing a rare species is far less likely to cause a problem than introducing a common one. In a new environment a rare species might thrive, but it will, because of its more limited gene pool, be less adaptable thanÂ a common species and so is unlikely to reach pest proportions.